1. Field of the Invention
The present invention relates to methods for producing olefins by catalytic decomposition of ether precursors, ethers, alcohols and mixtures thereof. Specifically, the present invention is directed to processes for regenerating catalysts and particularly decomposition catalysts used in methods for decompositions ethers, alcohols and mixtures thereof to produce olefins.
2. Discussion of Background and/or Material Information
Tertiary olefins are in general commercially produced by the sulfuric acid extraction of such olefins from mixtures containing them obtained e.g., by steam cracking of petroleum feeds.
Tertiary olefins may be prepared by reacting them selectively from such feeds with a primary alcohol in the presence of an acid catalyst to produce the corresponding alkyl tert-alkyl ethers; only the tert-alkyl ethers are formed since the secondary olefins react very slowly and the primary olefins are completely inert. Such alkyl tert-alkyl ethers may then be easily separated and subsequently decomposed back to the tertiary olefins and the primary alcohol.
Although it is disclosed that the clay of the catalyst is preferably washed first with water and then with methanol before calcining, this washing refers to that which is conducted after the clay is reacted with the acid, and does not refer to a washing which is conducted for the purpose of regenerating a deactivated catalyst which has been taken off-line due to becoming contaminated with foulants, after some time on stream.
U.S. Pat. No. 2,784,238, discloses regenerating a clay catalyst by washing the catalyst with a polar oxygenated solvent until the resins absorbed on the catalyst are dissolved. However, the clay catalyst is used in the production of resorcinals by the decompositions of hydroperoxides, and does not regenerate the catalyst in situ.
U.S. Pat. Nos. 3,472,786 and 4,469,805, disclosed the use of a methanol wash to regenerate clays used as absorbents for treating hydrocarbons; however, the clays are not disclosed as being useful as catalysts for any reaction.
Japanese Patent No. JP60-075331, discloses the regeneration of a layered clay catalyst by washing the clay with an aqueous mixture including 50-98% of an organic medium, such as methanol or ethanol, and discloses that the layered catalyst is for use in dewatering reactions, esterification, etherification and alkylization reactions.
Japanese Patent No. JP87-054540, washes a supported hydrogenation catalyst.
A number of methods have been proposed for producing tertiary olefins from alkyl tert-alkyl ethers using various catalysts.
U.S. Pat. No. 4,398,051, for example, uses aluminum compounds supported on silica or other carriers. U.S. Pat. No. 4,320,232 employs phosphoric acid on various supports. British Patent No. 1,173,128 uses metal-containing weakly acidic components on a carrier of 20M.sup.2 /gm surface area. U.S. Pat. No. 4,398,051 attempts to produce tertiary olefins from alkyl tert-alkyl ethers utilizing carriers alone in the decomposition of methyl tertiary butyl ether.
U.S. Pat. No. 4,691,073, MICHAELSON, discovered that high purity olefins are obtainable in extremely high yields over a sustained period by bringing alkyl tert-alkyl ethers into contact with a specified catalyst, i.e., clays treated with hydrofluoric acid and/or hydrochloric acid. Although a counter-flow stream of ether feed is disclosed, this is not done to substantially regenerate a catalyst in a fixed bed isothermal reactor.
It is known that tertiary olefins may be prepared by reacting them selectively from petroleum feeds with a primary alcohol in the presence of an acid catalyst to produce the corresponding alkyl tert alkyl ethers. Such alkyl tert-alkyl ethers may then be separated and subsequently decomposed back to the tertiary olefins and the primary alcohol.
U.S. Pat. No. 4,447,668, prepares isobutene or isoamolene from alkyl tertiary butyl ether or alkyl tertiary-amyl ether wherein a fixed bed cationic acidic exchange resin is used in a catalytic distillation process.
All these processes suffer from disadvantages. Among these disadvantages is that known catalysts do not have good catalyst life because higher temperatures, which eventually become limiting, are required to maintain high conversion of the alkyl tert-alkyl ethers. Additionally, larger amounts of the dialkyl ether by-product are produced as the catalyst ages with the disadvantage indicated above. This lack of good catalyst life may be due to the instability of the catalyst to high temperature being required for good conversion thus promoting fouling, to the catalyst itself promoting fouling, or to any or all of these. Also, a number of the catalysts, such as resins, cannot be regenerated after use.